Re: What is up with ISM?

>
>As far as Oracle is concerned, the main effect of ISM is to lock shared
>memory segments in RAM, so your SGA won't get paged out. In an ideal
>world, this won't make a big difference, because you'll have enough RAM to
>hold all your active processes and your SGA. Even in the real world, your
>SGA will usually get hit often enough to keep it in RAM, anyway, even
>though idle processes are getting swapped out. In general, if your SGA
>does get paged out, either it's too big, or you need more memory.
>
>IOW, ISM is nice, and its absence *might* be the cause of your performance
>problems, but it generally won't make that much difference, so I'd suggest
>that you look elsewhere.
>
>Lastly, ISM is only available on the Sun4m architecture because that's the
>only system that has the hardware to support it; AFAIK, it will never be
>available under Sun4u systems.

My experience confirms the problems that the original author found.

We just converted from a Sun Enterprise 150 with 256 megs of ram and a single processor to a Sun 3000 with 2 cpus and 512 megs of ram with Veritas using Oracle 7.3.x and performance dropped dramatically. After thrashing about trying to find the source of the problem, the tech support person from Oracle said that the
cause is the lack of intimate shared memory. The ENABLE_ISM parameter doesn't work in 2.6 and Sun and Oracle don't have a patch for it as yet.

It appears that throwing ram at the problem to prevent swapping is the solution. Received on Tue Jun 09 1998 - 00:00:00 CDT